The present invention relates to calibration for calculating the position and/or orientation of a camera. More specifically, the present invention relates to the technology of calibrating in a simple manner a camera mounted on a mobile object with high precision.
Conventionally, a system is known that monitors the surroundings of a vehicle by means of a camera mounted thereon. In such a monitoring system, a plurality of cameras are generally mounted on the vehicle so as to display a captured image on a monitor mounted inside the vehicle.
FIG. 23 is a block diagram showing the structure of a conventional vehicle surrounding monitoring system (Japanese Laid-Open Publication No. 3-99952). In FIG. 23, an image converting section 1202 receives the respective images from a plurality of cameras 1201 mounted on the vehicle to produce a synthesized image as viewed from a virtual view point by perspective transformation. An image display portion 1203 displays the synthesized image on a TV monitor 1204 installed at, e.g., the driver""s seat. When the virtual view point is oriented downward at the upper central position of the vehicle, the driver can instantly see the situations at and around the vehicle from the TV monitor 1204, resulting in improved safety of the driving.
(Problems)
The aforementioned monitoring system joins a plurality of camera images into a single image. In order to avoid any displacement at each boundary between the joined images, it is necessary to calculate in advance the orientation and position of each camera accurately. This calculation is referred to as camera calibration.
For example, in a known calibration method, feature points each having a known coordinate position in a prescribed coordinate system are captured with respective cameras in order to produce a set of data having the coordinates of each feature point on the camera image mapped with its actual spatial coordinates, i.e., calibration data. Calibration is conducted using the calibration data thus produced. Since this calibration method is described in detail in, e.g., Matsuyama et al., xe2x80x9cComputer Vision: Gijyutsu Hyouron To Syourai Tenbou (Technical Review and Future Outlook)xe2x80x9d (Shin-gijyutsu Communications, pp. 37-53, June 1998), description thereof is herein omitted.
For example, the following technologies are known regarding camera calibration: technology of calibrating a visual sensor system of a transfer line by means of a special jig (disclosed in Japanese Publication for Opposition No. 7-90494); and technology of obtaining an installation error of fixed three-dimensional visual means in a robot coordinate system in a robot handling apparatus (disclosed in Japanese Publication for Opposition No. 7-27408). However, no effective calibration technology has been established for the cameras mounted on mobile objects such as vehicles.
Moreover, in order to calibrate the cameras having a wide monitoring range such as those for vehicle monitoring, feature points must be widely distributed throughout the camera""s monitoring range. This requirement may be satisfied by installation of huge equipment having such feature points. However, this is not preferable since a large site and extremely high costs are required. Moreover, if such equipment is installed at a certain location, a vehicle must be moved all the way to the location for camera calibration, resulting in significant inconvenience. Since it is expected that the vehicle surrounding monitoring systems be widely used in the future, development of a simple camera calibration method is of urgent necessity in view to exchange or addition of the camera and a possibility of frequent positional displacement of the camera due to a traffic accident or vehicle running.
It is an object of the present invention to enable simple high-precision calibration of a camera mounted on a mobile object.
More specifically, a calibration system according to the present invention includes: a mobile object having a camera mounted thereon; a target apparatus for calibrating the camera; and a positioning means provided to at least one of the mobile object ant the target apparatus for fixing a positional relation between the mobile object and the target apparatus to a prescribed relation.
According to the present invention, the positional relation between the mobile object and the target apparatus can be fixed to the prescribed relation by the positioning means. As a result, the mobile object need no longer be accurately positioned for camera calibration. Accordingly, calibration of the camera mounted on the mobile object is simplified.
In the calibration system of the present invention, the positioning means has a joint means for physically fixing the target apparatus to the mobile object.
In the calibration system of the present invention, the positioning means has a scope means provided to one of the mobile object and the target apparatus for positioning the target apparatus with reference to a target point located on the other.
In the calibration system of the present invention, the target apparatus has a feature point capable of emitting light under external control, and the mobile object includes a control means for controlling the light emission of the feature point of the target apparatus.
According to the present invention, a calibration system includes: a mobile object having a camera mounted thereon; a target apparatus for calibrating the camera; and a positional-relation estimating means provided to at least one of the mobile object ant the target apparatus for obtaining a positional relation between the mobile object and the target apparatus.
According to the present invention, the positional relation between the mobile object and the target apparatus is obtained by the positional-relation estimating means. As a result, the mobile object need no longer be accurately positioned for camera calibration. Accordingly, calibration of the camera mounted on the mobile object is simplified.
In the calibration system of the present invention, the positional-relation estimating means has a target data obtaining means provided to one of the mobile object and the target apparatus for obtaining a coordinate value of a target point located on the other in a coordinate system in the one with reference to the target point.
A target apparatus for calibrating a camera mounted on a mobile object according to the present invention includes a positioning means for fixing a positional relation between the mobile object and the target apparatus to a prescribed relation.
A target apparatus for calibrating a camera mounted on a mobile object according to the present invention includes a positional-relation estimating means for obtaining a positional relation between the mobile object and the target apparatus.
A method for calibrating a camera mounted on a mobile object according to the present invention includes the steps of: preparing a target apparatus for calibration around the mobile object; fixing a position of the target apparatus such that the target apparatus has a prescribed positional relation with the mobile object, by using a positioning means provided to at least one of the mobile object and the target apparatus; and capturing a feature point of the target apparatus with the camera, wherein the camera is calibrated based on a relation between image coordinates of the feature point and real-world coordinates thereof.
A method for calibrating a camera mounted on a mobile object according to the present invention includes the steps of: preparing a target apparatus for calibration around the mobile object; obtaining a positional relation between the target apparatus and the mobile object by using a positional-relation estimating means provided to at least one of the mobile object and the target apparatus; and capturing a feature point of the target apparatus with the camera, wherein the camera is calibrated based on image coordinates of the feature point, real-world coordinates of the feature point based on the target apparatus, and the obtained positional relation between the target apparatus and the mobile object.